Imprint lithography

ABSTRACT

A method for manufacturing a working template for use in imprint lithography is disclosed, which in an embodiment, involves contacting a first target region of an imprintable medium on a working template substrate with a master template to form a first imprint in the medium, the imprint defining a part of a working template pattern, separating the master template from the imprinted medium, contacting a second target region of the medium with the master template to form a second imprint in the medium, the second imprint defining a further part of the working template pattern, and separating the master template from the imprinted medium.

FIELD

The invention relates to imprint lithography.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus areconventionally used, for example, in the manufacture of integratedcircuits (ICs), flat panel displays and other devices involving finestructures.

It is desirable to reduce the size of features in a lithographic patternbecause this allows for a greater density of features on a givensubstrate area. In photolithography, the increased resolution may beachieved by using radiation of a short wavelength. However, there areproblems associated with such reductions. Lithographic apparatus using193 nm wavelength radiation are starting to be adopted but even at thislevel, diffraction limitations may become a barrier. At lowerwavelengths, the transparency of projection system materials is poor.Thus, optical lithography capable of enhanced resolution will likelyrequire complex optics and rare materials and thus will be expensive.

An alternative method to printing sub-100 nm features, known as imprintlithography, comprises transferring a pattern to a substrate byimprinting a pattern into an imprintable medium using a physical mouldor template. The imprintable medium may be the substrate or a materialcoated onto a surface of the substrate. The imprintable medium may befunctional or may be used as a “mask” to transfer a pattern to anunderlying surface. The imprintable medium may, for instance, beprovided as a resist deposited on a substrate, such as a semiconductormaterial, to which the pattern defined by the template is to betransferred. Imprint lithography is thus essentially a moulding processon a micrometer or nanometer scale in which the topography of a templatedefines the patterns created on a substrate. Patterns may be layered aswith optical lithography processes so that in principle imprintlithography could be used for such applications as integrated circuitmanufacture.

The resolution of imprint lithography is limited only by the resolutionof the template fabrication process. For instance, imprint lithographyhas been used to produce features in the sub-50 nm range with goodresolution and line edge roughness. In addition, imprint processes maynot require the expensive optics, advanced illumination sources orspecialized resist materials typically required for optical lithographyprocesses.

SUMMARY

According to an aspect of the invention, there is provided a method formanufacturing a working template for use in imprint lithography,comprising:

contacting a first target region of an imprintable medium on a workingtemplate substrate with a master template to form a first imprint in themedium, the imprint defining a part of a working template pattern;

separating the master template from the imprinted medium;

contacting a second target region of the medium with the master templateto form a second imprint in the medium, the second imprint defining afurther part of the working template pattern; and

separating the master template from the imprinted medium.

According to an aspect of the invention, there is provided a method formanufacturing a working template for use in imprint lithography,comprising:

contacting a first target region of an imprintable medium on a workingtemplate substrate with a master template to form a first imprint in themedium, the first imprint comprising a first pattern feature and a firstarea of reduced thickness and defining a part of a working templatepattern;

separating the master template from the imprinted medium;

contacting a second target region of the medium with the master templateto form a second imprint in the medium, the second imprint comprising asecond pattern feature and a second area of reduced thickness anddefining a further part of the working template pattern;

separating the master template from the imprinted medium;

etching the first and second areas of reduced thickness to exposeregions of the working template substrate; and

etching the exposed regions of the working template substrate to formthe working template pattern in the working template substrate to definea working template.

Thus, in an embodiment, a smaller master template may be repeatedlyimprinted in to an imprintable medium which is then processed to form alarger ‘modular’ pattern in a working template substrate. In this way,the expense connected with the manufacture of the initial mastertemplate employing e-beam etching may be reduced. Additionally, sincethe master template may be imprinted into the imprintable medium anydesirable number of times, relatively large working template may becheaply and easily produced.

According to an aspect of the invention, there is provided a method formanufacturing a photo transparent working template for use in imprintlithography, comprising:

contacting a target region of an imprintable medium on a phototransparent working template substrate with a master template to form animprint defining a working template pattern in the medium; and

separating the master template from the imprinted medium to provide aphoto transparent working template.

According to an aspect of the invention, there is provided a method formanufacturing a photo transparent working template for use in imprintlithography, comprising:

contacting a target region of an imprintable medium on a phototransparent working template substrate with a master template to form animprint defining a working template pattern in the medium, the imprintcomprising a pattern feature and an area of reduced thickness;

separating the master template from the imprinted medium;

etching the area of reduced thickness to expose a region of the phototransparent working template substrate; and

etching the exposed region of the photo transparent working templatesubstrate to form the working template pattern in the photo transparentworking template substrate to define a photo transparent workingtemplate.

According to an aspect of the invention, there is provided an imprintingmethod, comprising:

contacting a first target region of a first imprintable medium on aworking template substrate with a master template to form an imprint inthe first medium, the imprint defining a part of a working templatepattern;

separating the master template from the imprinted first medium;

contacting a second target region of the first medium with the mastertemplate to form a second imprint in the first medium, the secondimprint defining a further part of the working template pattern;

separating the master template from the imprinted first medium toprovide a working template;

contacting a second imprintable medium on a device substrate with theworking template to form an imprint in the second medium correspondingto the working template pattern; and

separating the working template from the imprinted second medium.

According to an aspect of the invention, there is provided an imprintingmethod, comprising:

contacting a first target region of a first imprintable medium on aworking template substrate with a master template to form a firstimprint in the first medium, the first imprint comprising a firstpattern feature and a first area of reduced thickness and defining apart of a working template pattern;

separating the master template from the imprinted first medium;

contacting a second target region of the first medium with the mastertemplate to form a second imprint in the first medium, the secondimprint comprising a second pattern feature and a second area of reducedthickness and defining a further part of the working template pattern;

separating the master template from the imprinted first medium;

etching the first and second areas of reduced thickness to exposeregions of the working template substrate;

etching the exposed regions of the working template substrate to formthe working template pattern in the working template substrate to definea working template;

contacting a second imprintable medium on a device substrate with theworking template to form an imprint in the second medium correspondingto the working template pattern; and

separating the working template from the imprinted second medium.

According to an aspect of the invention, there is provided a method forpatterning a device substrate, comprising:

contacting a first target region of a first imprintable medium on aworking template substrate with a master template to form a firstimprint in the first medium, the first imprint defining a part of aworking template pattern;

separating the master template from the imprinted first medium;

contacting a second target region of the first medium with the mastertemplate to form a second imprint in the first medium, the secondimprint defining a further part of the working template pattern;

separating the master template from the imprinted first medium toprovide a working template;

contacting a second imprintable medium on a device substrate with theworking template to form an imprint in the second medium correspondingto the working template pattern, the imprint in the second mediumcomprising a pattern feature and an area of reduced thickness;

separating the working template from the imprinted second medium;

etching the area of reduced thickness of the imprint in the secondmedium to expose a region of the device substrate; and

etching the exposed region of the device substrate to form the workingtemplate pattern in the device substrate.

According to an aspect of the invention, there is provided a method forpatterning a device substrate, comprising:

contacting a first target region of a first imprintable medium on aworking template substrate with a master template to form a firstimprint in the first medium, the first imprint comprising a firstpattern feature and a first area of reduced thickness and defining apart of a working template pattern;

separating the master template from the imprinted first medium;

contacting a second target region of the first medium with the mastertemplate to form a second imprint in the first medium, the secondimprint comprising a second pattern feature and a second area of reducedthickness and defining a further part of the working template pattern;

separating the master template from the imprinted first medium;

etching the first and second areas of reduced thickness to exposeregions of the working template substrate;

etching the exposed regions of the working template substrate to formthe working template pattern in the working template substrate to definea working template;

contacting a second imprintable medium on a device substrate with theworking template to form an imprint in the second medium correspondingto the working template pattern, the imprint in the second mediumcomprising a pattern feature and an area of reduced thickness;

separating the working template from the imprinted second medium;

etching the area of reduced thickness of the imprint in the secondmedium to expose a region of the device substrate; and

etching the exposed region of the device substrate to form the workingtemplate pattern in the device substrate.

According to an aspect of the invention, there is provided a workingtemplate manufacturing apparatus, comprising:

a substrate holder configured to hold a substrate having a imprintablemedium thereon;

a template holder configured to cause a master template supported by thetemplate holder to contact the imprintable medium to form a firstimprint in the medium, the first imprint defining a part of a workingtemplate pattern, to cause the master template to contact theimprintable medium to form a second imprint in the medium, the secondimprint defining a further part of the working template pattern, and tocause the master template to separate from the imprinted medium; and

an etching apparatus.

According to an aspect of the invention, there is provided a workingtemplate manufacturing apparatus, comprising:

a substrate holder configured to hold a substrate having a imprintablemedium thereon;

a template holder configured to cause a master template supported by thetemplate holder to contact the imprintable medium to form a firstimprint in the medium, the first imprint comprising a first patternfeature and a first area of reduced thickness and defining a part of aworking template pattern, to cause the master template to contact theimprintable medium to form a second imprint in the medium, the secondimprint comprising a second pattern feature and a second area of reducedthickness and defining a further part of the working template pattern,and to cause the master template to separate from the imprinted medium;and

an etching apparatus configured to etch the first and second areas ofreduced thickness to expose regions of the working template substrateand to etch the exposed regions of the working template substrate toform the final pattern in the working template substrate to define aworking template.

In respect of the aforementioned aspects of the invention, in anembodiment, the target regions are laterally spaced from one another. Inan embodiment, the target regions are provided separately on the workingtemplate substrate.

In an embodiment, the working template substrate is photo transparent.In an embodiment, the working template substrate comprises siliconand/or quartz.

Conveniently, the exposed regions of the working template substrate maybe etched using an etchant selected from a group consisting of: CHF₃,CF₄, O₂, Cl₂, HBr and SF₆.

In an embodiment, the imprintable medium is selected from a groupconsisting of: a photo (e.g. UV) curable material, a thermally curablematerial and a thermoplastic polymer material. In an embodiment, theimprintable medium is in a flowable state when contacted by the masteror working template and is solidified prior to separation from themaster or working template. Depending upon which material is chosen asthe imprintable medium, the method forming one of the above aspects ofthe invention may additionally comprise solidifying the imprintablemedium by the provision of photo radiation, heat (e.g. to cross link athermally crosslinkable polymer, such as a thermosetting resin) orcooling (e.g. to below the glass transition temperature of athermoplastic polymer).

In an embodiment, an intermediate layer (which may comprise a materialselected from a group consisting of: chromium, an oxide and a nitride)is provided between the working template substrate and the imprintablemedium. In an embodiment, etching an area of reduced thickness definedin the imprintable medium exposes a region of the intermediate layer andthe method may further comprise etching the exposed region of theintermediate layer to expose a region of the working template substrate.In this case, the method may further comprise etching (for example, byusing an etchant selected from a group consisting of: hydrofluoric acid,O₂ and Cl₂) the exposed region of the working template substrate to formthe working template pattern in the working template substrate to definethe working template.

In an embodiment, the working template pattern covers substantially allof a surface of the working template substrate. The area of imprintformed in the imprintable medium by contact of the master template mayrepresent up to 50% of the area of the working template pattern. In anembodiment, the area of the imprint may represent up to 25% or up to 10%of the area of the working template pattern.

In an embodiment, the master template has been produced using a methodemploying e-beam etching.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 a-1 c illustrate examples of soft, hot and UV lithography processrespectively;

FIG. 2 illustrates a two step etching process employed when hot and UVimprint lithography is used to pattern a resist layer;

FIG. 3 illustrates relative dimensions of template features compared tothe thickness of a typical imprintable resist layer deposited on asubstrate;

FIG. 4 illustrates manufacture of a working template in accordance withan embodiment of the invention; and

FIG. 5 is a schematic representation of an imprint system incorporatinga gas bearing.

DETAILED DESCRIPTION

There are two principal approaches to imprint lithography which will betermed generally as hot imprint lithography and UV imprint lithography.There is also a third type of “printing” lithography known as softlithography. Examples of these are illustrated in FIGS. 1 a to 1 c.

FIG. 1 a schematically depicts the soft lithography process whichinvolves transferring a layer of molecules 11 (typically an ink such asa thiol) from a flexible template 10 (typically fabricated frompolydimethylsiloxane (PDMS)) onto a resist layer 13 which is supportedupon a substrate 12 and planarization and transfer layer 12′. Thetemplate 10 has a pattern of features on its surface, the molecularlayer being disposed upon the features. When the template is pressedagainst the resist layer, the layer of molecules 11 stick to the resist.Upon removal of the template from the resist, the layer of molecules 11stick to the resist, the residual layer of resist is etched such thatthe areas of the resist not covered by the transferred molecular layerare etched down to the substrate.

The template used in soft lithography may be easily deformed and maytherefore not be suited to high resolution applications, e.g. on ananometer scale, since the deformation of the template may adverselyaffect the imprinted pattern. Furthermore, when fabricating multiplelayer structures, in which the same region will be overlaid multipletimes, soft imprint lithography may not provide overlay accuracy on ananometer scale.

Hot imprint lithography (or hot embossing) is also known as nanoimprintlithography (NIL) when used on a nanometer scale. The process uses aharder template made from, for example, silicon or nickel, which aremore resistant to wear and deformation. This is described for instancein U.S. Pat. No. 6,482,742 and illustrated in FIG. 1 b. In a typical hotimprint process, a solid template 14 is imprinted into a thermosettingor a thermoplastic polymer resin 15, which has been cast on the surfaceof substrate. The resin may, for instance, be spin coated and baked ontothe substrate surface or more typically (as in the example illustrated)onto a planarization and transfer layer 12′. It should be understoodthat the term “hard” when describing an imprint template includesmaterials which may generally be considered between “hard” and “soft”materials, such as for example “hard” rubber. The suitability of aparticular material for use as an imprint template is determined by itsapplication requirements.

When a thermosetting polymer resin is used, the resin is heated to atemperature such that, upon contact with the template, the resin issufficiently flowable to flow into the pattern features defined on thetemplate. The temperature of the resin is then increased to thermallycure (e.g. crosslink) the resin so that it solidifies and irreversiblyadopts the desired pattern. The template may then be removed and thepatterned resin cooled.

Examples of thermoplastic polymer resins used in hot imprint lithographyprocesses are poly (methyl methacrylate), polystyrene, poly (benzylmethacrylate) or poly (cyclohexyl methacrylate). The thermoplastic resinis heated so that it is in a freely flowable state immediately prior toimprinting with the template. It is typically necessary to heatthermoplastic resin to a temperature considerably above the glasstransition temperature of the resin. The template is pressed into theflowable resin and sufficient pressure is applied to ensure the resinflows into all the pattern features defined on the template. The resinis then cooled to below its glass transition temperature with thetemplate in place whereupon the resin irreversibly adopts the desiredpattern. The pattern will consist of the features in relief from aresidual layer of the resin which may then be removed by an appropriateetch process to leave only the pattern features.

Upon removal of the template from the solidified resin, a two-stepetching process is typically performed as illustrated in FIGS. 2 a to 2c. The substrate 20 has a planarization and transfer layer 21immediately upon it, as shown in FIG. 2 a. The purpose of theplanarization and transfer layer is twofold. It acts to provide asurface substantially parallel to that of the template, which helpsensure that the contact between the template and the resin is parallel,and also to improve the aspect ratio of the printed features, as will bedescribed below.

After the template has been removed, a residual layer 22 of thesolidified resin is left on the planarization and transfer layer 21,shaped in the desired pattern. The first etch is isotropic and removesparts of the residual layer 22, resulting in a poor aspect ratio offeatures where L1 is the height of the features 23, as shown in FIG. 2b. The second etch is anisotropic (or selective) and improves the aspectratio. The anisotropic etch removes those parts of the planarization andtransfer layer 21 which are not covered by the solidified resin,increasing the aspect ratio of the features 23 to (L2/D), as shown inFIG. 2 c. The resulting polymer thickness contrast left on the substrateafter etching can be used as for instance a mask for dry etching if theimprinted polymer is sufficiently resistant, for instance as a step in alift-off process.

Hot imprint lithography suffers from a disadvantage in that not onlymust the pattern transfer be performed at a higher temperature, but alsorelatively large temperature differentials might be required in order toensure the resin is adequately solidified before the template isremoved. Temperature differentials between 35 and 100° C. may be needed.Differential thermal expansion between, for instance, the substrate andtemplate may then lead to distortion in the transferred pattern. Thismay be exacerbated by the relatively high pressure required for theimprinting step, due the viscous nature of the imprintable material,which can induce mechanical deformation in the substrate, againdistorting the pattern.

UV imprint lithography, on the other hand, does not involve such hightemperatures and temperature changes nor does it require such viscousimprintable materials. Rather, UV imprint lithography involves the useof a partially or wholly transparent template and a UV-curable liquid,typically a monomer such as an acrylate or methacrylate. In general, anyphotopolymerisable material could be used, such as a mixture of monomersand an initiator. The curable liquid may also, for instance, include adimethyl siloxane derivative. Such materials are less viscous than thethermosetting and thermoplastic resins used in hot imprint lithographyand consequently move much faster to fill template pattern features. Lowtemperature and low pressure operation also favors higher throughputcapabilities.

An example of a UV imprint process is illustrated in FIG. 1 c. A quartztemplate 16 is applied to a UV curable resin 17 in a similar manner tothe process of FIG. 1 b. Instead of raising the temperature as in hotembossing employing thermosetting resins, or temperature cycling whenusing thermoplastic resins, UV radiation is applied to the resin throughthe quartz template in order to polymerise and thus cure it. Uponremoval of the template, the remaining steps of etching the residuallayer of resist are the same or similar as for the hot embossing processdescribed above. The UV curable resins typically used have a much lowerviscosity than typical thermoplastic resins so that lower imprintpressures can be used. Reduced physical deformation due to the lowerpressures, together with reduced deformation due to high temperaturesand temperature changes, makes UV imprint lithography suited toapplications requiring high overlay accuracy. In addition, thetransparent nature of UV imprint templates can accommodate opticalalignment techniques simultaneously to the imprinting.

Although this type of imprint lithography mainly uses UV curablematerials, and is thus generically referred to as UV imprintlithography, other wavelengths of radiation may be used to cureappropriately selected materials (e.g., activate a polymerization orcross linking reaction). In general, any radiation capable of initiatingsuch a chemical reaction may be used if an appropriate imprintablematerial is available. Alternative “activating radiation” may, forinstance, include visible light, infrared radiation, x-ray radiation andelectron beam radiation. In the general description above, and below,references to UV imprint lithography and use of UV radiation are notintended to exclude these and other activating radiation possibilities.

As an alternative to imprint systems using a planar template which ismaintained substantially parallel to the substrate surface, rollerimprint systems have been developed. Both hot and UV roller imprintsystems have been proposed in which the template is formed on a rollerbut otherwise the imprint process is very similar to imprinting using aplanar template. Unless the context requires otherwise, references to animprint template include references to a roller template.

There is a particular development of UV imprint technology known as stepand flash imprint lithography (SFIL) which may be used to pattern asubstrate in small steps in a similar manner to optical steppersconventionally used, for example, in IC manufacture. This involvesprinting small areas of the substrate at a time by imprinting a templateinto a UV curable resin, ‘flashing’ UV radiation through the template tocure the resin beneath the template, removing the template, stepping toan adjacent region of the substrate and repeating the operation. Thesmall field size of such step and repeat processes may help reducepattern distortions and CD variations so that SFIL may be particularlysuited to manufacture of IC and other devices requiring high overlayaccuracy.

Although in principle the UV curable resin can be applied to the entiresubstrate surface, for instance by spin coating, this may be problematicdue to the volatile nature of UV curable resins.

One approach to addressing this problem is the so-called ‘drop ondemand’ process in which the resin is dispensed onto a target portion ofthe substrate in droplets immediately prior to imprinting with thetemplate. The liquid dispensing is controlled so that a predeterminedvolume of liquid is deposited on a particular target portion of thesubstrate. The liquid may be dispensed in a variety of patterns and thecombination of carefully controlling liquid volume and placement of thepattern can be employed to confine patterning to the target area.

Dispensing the resin on demand as mentioned is not a trivial matter. Thesize and spacing of the droplets are carefully controlled to ensurethere is sufficient resin to fill template features while at the sametime minimizing excess resin which can be rolled to an undesirably thickor uneven residual layer since as soon as neighboring drops touch theresin will have nowhere to flow.

Although reference is made above to depositing UV curable liquids onto asubstrate, the liquids could also be deposited on the template and ingeneral the same techniques and considerations will apply.

FIG. 3 illustrates the relative dimensions of the template, imprintablematerial (curable monomer, thermosetting resin, thermoplastic, etc.),and substrate. The ratio of the width of the substrate, D, to thethickness of the curable resin layer, t, is of the order of 10⁶. It willbe appreciated that, in order to avoid the features projecting from thetemplate damaging the substrate, the dimension t should be greater thanthe depth of the projecting features on the template.

The residual layer of imprintable material left after stamping is usefulin protecting the underlying substrate, but may also impact obtaininghigh resolution and/or overlay accuracy. The first ‘breakthrough’ etchis isotropic (non-selective) and will thus to some extent erode thefeatures imprinted as well as the residual layer. This may beexacerbated if the residual layer is overly thick and/or uneven.

This etching may, for instance, lead to a variation in the thickness offeatures ultimately formed on the underlying substrate (i.e. variationin the critical dimension). The uniformity of the thickness of a featurethat is etched in the transfer layer in the second anisotropic etch isdependant upon the aspect ratio and integrity of the shape of thefeature left in the resin. If the residual resin layer is uneven, thenthe non-selective first etch may leave some of these features with“rounded” tops so that they are not sufficiently well defined to ensuregood uniformity of feature thickness in the second and any subsequentetch process.

In principle, the above problem may be reduced by ensuring the residuallayer is as thin as possible but this may require application ofundesirably large pressures (possibly increasing substrate deformation)and relatively long imprinting times (perhaps reducing throughput).

As noted above, the resolution of the features on the template surfaceis a limiting factor on the attainable resolution of features printed onthe substrate. The templates used for hot and UV imprint lithography aregenerally formed in a two-stage process. Initially, the required patternis written using, for example, electron beam writing to give a highresolution pattern in resist. The resist pattern is then transferredinto a thin layer of chrome which forms the mask for the final,anisotropic etch step to transfer the pattern into the base material ofthe template. Other techniques such as for example ion-beam lithography,X-ray lithography, extreme UV lithography, epitaxial growth, thin filmdeposition, chemical etching, plasma etching, ion etching or ion millingcould be used. Generally, a technique capable of very high resolutionwill be desired as the template is effectively a 1× mask with theresolution of the transferred pattern being limited by the resolution ofthe pattern on the template.

The release characteristics of the template are also a consideration.The template may, for instance, be treated with a surface treatmentmaterial to form a thin release layer on the template having a lowsurface energy (a thin release layer may also be deposited on thesubstrate).

Another consideration in the development of imprint lithography is themechanical durability of the template. The template may be subjected tolarge forces during stamping of the imprintable medium, and in the caseof hot imprint lithography, it may also be subjected to high pressureand temperature. The force, pressure and/or temperature may causewearing of the template, and may adversely affect the shape of thepattern imprinted upon the substrate.

In hot imprint lithography, a potential advantage may be realized inusing a template of the same or similar material to the substrate to bepatterned in order to help reduce differential thermal expansion betweenthe two. In UV imprint lithography, the template is at least partiallytransparent to the activation radiation and accordingly quartz templatesare used.

Although specific reference may be made in this text to the use ofimprint lithography in the manufacture of ICs, it should be understoodthat imprint apparatus and methods described may have otherapplications, such as the manufacture of integrated optical systems,guidance and detection patterns for magnetic domain memories, hard diskmagnetic media, flat panel displays, thin-film magnetic heads, etc.

While in the description above particular reference has been made to theuse of imprint lithography to transfer a template pattern to a substratevia an imprintable resin effectively acting as a resist, in somecircumstances the imprintable material may itself be a functionalmaterial, for instance having a functionally such as conductivity,optical linear or non linear response, etc. For example, the functionalmaterial may form a conductive layer, a semiconductive layer, adielectric layer or a layer having another desirable mechanical,electrical or optical property. Some organic substances may also beappropriate functional materials. Such applications may be within thescope of one or more embodiments of the invention.

Although imprint lithography theoretically provides many benefits overconventional optical lithography, in order for it to be adopted widelyin industry it should be economically viable. The costs involved areprimarily determined by the costs of the tooling and templatemanufacture, and the production efficiency or throughput. In spite ofthe expectation that tooling costs will be relatively low, this may bemore than offset by the fact that template production costs are likelyto be relatively high since the template is necessarily the same size asthe pattern to be imprinted into the substrate (imprint lithographybeing a 1× process). When a single volume of an imprintable medium isprovided on a substrate surface, the imprinting time is largelydependent upon the template area. In essence, as the area of thetemplate increases the imprinting time decreases. Thus, designing aneconomically viable imprinting process is problematic because of theneed to find a balance between the high costs involved in producinglarger 1× templates and the desire to reduce imprinting times byemploying larger templates.

FIG. 4 shows a quartz master template 40, previously fabricated using aconventional technique involving e-beam etching, being imprinted into afirst target region of a volume of a thermoplastic imprintable medium 41shown on the left of FIG. 4. The imprintable medium 41 is supported onan intermediate layer (e.g., of chromium) 42 which is itself supportedon a quartz working template substrate layer 43. The master template 40defines a portion of a final pattern which is to be imprinted into thetemplate substrate 43 and which can then be imprinted into a devicesubstrate. Contacting the imprintable medium 41 with the master templateforms a plurality of upstanding pattern features 44 and areas of reducedthickness 45. The master template 40 is then separated from the firsttarget region of the imprintable medium 41 and imprinted into a secondtarget region of the medium 41, shown on the right of FIG. 4, so as toform an identical arrangement of pattern features and areas of reducedthickness as were formed in the first target region.

Once the complete final pattern has been formed in the layer ofimprintable medium 41, a first etch removes the exposed regions of theintermediate layer 42 and a second etch removes the exposed regions 46of the template substrate layer 43 so as to form pattern features 47 andareas of reduced thickness 48 defining the final pattern in the templatesubstrate layer 43. To complete the process, the layers of imprintablemedium 41 and intermediate layer 42 lying directly above the patternfeatures 47 in the template substrate layer 43 are removing by aconventional technique.

Following manufacture of the patterned working template, it can then beused in subsequent processing steps to pattern device substrates withthe complete final pattern.

The size and arrangement of the pattern may of course be chosen to suitany particular application. Moreover, the master template may beimprinted any suitable number of times to provide the desired finalpattern. The different target areas of imprintable medium may be locatedin any appropriate way on the substrate surface, for example they may beadjacent one another as shown in FIG. 4, or they may be spaced apart.

The cost and complexity of the imprint process may also be increased asa result of the desire to operate the process under vacuum and/or highimprinting pressure to avoid problems relating to gas (e.g., air) beingtrapped within the imprinted medium. It is envisaged that a relativelycheap and simple way to reduce costs in this regard would be to providea localized low pressure channel (or perhaps a vacuum channel) aroundthe imprint area. A suitable arrangement is shown schematically in FIG.5.

FIG. 5 shows a template 50 to be used to pattern a substrate 51. Thetemplate 50 is supported on a pair of plate springs 52 which areconnected to arms 53 mounted on piezo actuators 54. Laterally outward ofthe arms 53 is a low pressure channel 55, laterally outward of the lowpressure channel 55 is a neutral pressure channel 56, and laterallyoutward of the neutral pressure channel 56 is a high pressure channel57. The pressure differential produced between the three channels 55,56, 57 causes the template 50 to float a predefined distance above thesurface of a volume of imprintable medium (not shown) provided on thesurface of the substrate 51. By controlling the pressure differential,the imprinting and separation processes can be controlled. For example,by decreasing pressure in the high pressure channel 57, the template 50can be caused to contact the medium, and by increasing pressure in thehigh pressure channel 57, the template 50 can be caused to separate fromthe medium. Optionally, the space 58 below the template 50 can also beoperated at low pressure or vacuum. The large low pressure area thuscreated can be used as (part of) the preload of a gas bearing employedin the imprinting process. It will be evident to the skilled person thatsuch a system provides a relatively simple solution to the problem ofgas bubbles being entrapped within the imprintable medium.

The provision of such a low pressure channel around the imprinting areaalso may have a benefit in the fabrication of optical structures inwhich the inclusion of gas bubbles may cause yield problems.

The concept of employing a low pressure channel around the imprintingarea provides a further benefit. During imprinting, an amount ofimprintable medium is squeezed out from under the template until thedesired template/substrate gap is obtained (e.g. 50 nm). Many imprintprocesses are carried out at atmospheric pressure and so a component ofthe force applied to the template to imprint the desired pattern isprovided to ensure sufficient excess imprintable medium is squeezed out.Provision of a low pressure channel around the imprinting area mayenable the excess imprintable medium to be squeezed out from under thetemplate more easily and consequently reduce the component of theimprinting force required to squeeze out the excess medium. Anadditional advantage of this method is that it may even out any pressureimbalance between the template and the imprintable medium. This methodshould increase imprinting times and reduce mechanical distortionsduring the imprinting process.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

1-44. (canceled)
 45. A working template manufacturing apparatus,comprising: a substrate holder configured to hold a working templatesubstrate having a imprintable medium thereon; and a template holderconfigured to cause a master template supported by the template holderto contact the imprintable medium to form a first imprint in the medium,the first imprint defining a part of a working template pattern, tocause the master template to contact the imprintable medium to form asecond imprint in the medium, the second imprint defining a further partof the working template pattern, and to cause the master template toseparate from the imprinted medium, wherein the working template patternis configured to imprint a pattern on a device substrate.
 46. Theapparatus according to claim 45, further comprising a dosing apparatusconfigured to provide a volume of the imprintable medium on the workingtemplate substrate.
 47. A working template manufacturing apparatus,comprising: a substrate holder configured to hold a working templatesubstrate having a imprintable medium thereon; a template holderconfigured to cause a master template supported by the template holderto contact the imprintable medium to form a first imprint in the medium,the first imprint comprising a first pattern feature and a first area ofreduced thickness and defining a part of a working template pattern, tocause the master template to contact the imprintable medium to form asecond imprint in the medium, the second imprint comprising a secondpattern feature and a second area of reduced thickness and defining afurther part of the working template pattern, and to cause the mastertemplate to separate from the imprinted medium; and an etching apparatusconfigured to etch the first and second areas of reduced thickness toexpose regions of the working template substrate and to etch the exposedregions of the working template substrate to form the working templatepattern in the working template substrate to define a working templateconfigured to imprint a pattern on a device substrate.
 48. The apparatusaccording to claim 47, further comprising a dosing apparatus configuredto provide a volume of the imprintable medium on the working templatesubstrate.
 49. The apparatus according to claim 47, wherein the firstimprint and the second imprint are laterally spaced from one another.50. The apparatus according to claim 47, wherein the working templatesubstrate is photo transparent.
 51. The apparatus according to claim 47,wherein the etching apparatus is configured to etch the exposed regionsof the working template substrate using an etchant selected from a groupconsisting of: CHF₃, CF₄, O₂, Cl₂, HBr and SF₆.
 52. The apparatusaccording to claim 47, wherein an intermediate layer is provided betweenthe working template substrate and the imprintable medium.
 53. Theapparatus according to claim 52, wherein etch of the first and secondareas of reduced thickness exposes regions of the intermediate layer andthe etching apparatus is configured to etch the exposed regions of theintermediate layer to expose a region of the working template substrate.54. The apparatus according to claim 53, wherein the etching apparatusis configured to etch the exposed regions of the working templatesubstrate to form the working template pattern in the working templatesubstrate to define the working template.
 55. The apparatus according toclaim 53, wherein the etching apparatus is configured to etch theexposed regions of the intermediate layer using an etchant selected froma group consisting of: hydrofluoric acid, O₂ and Cl₂.
 56. The apparatusaccording to claim 52, wherein the intermediate layer comprises amaterial selected from a group consisting of: chromium, an oxide and anitride.
 57. The apparatus according to claim 45, further comprising anetching apparatus.
 58. The apparatus according to claim 45, wherein thefirst imprint and the second imprint are laterally spaced from oneanother.
 59. The apparatus according to claim 45, wherein the workingtemplate substrate is photo transparent.
 60. The apparatus according toclaim 45, wherein an intermediate layer is provided between the workingtemplate substrate and the imprintable medium.
 61. The apparatusaccording to claim 60, wherein the intermediate layer comprises amaterial selected from a group consisting of: chromium, an oxide and anitride.
 62. A manufacturing apparatus, comprising: a substrate holderconfigured to hold a working template substrate having a imprintablemedium thereon; and a template holder configured to cause a mastertemplate supported by the template holder to contact the imprintablemedium to form a first imprint in the medium, the first imprint defininga part of a working template pattern, to cause the master template tocontact the imprintable medium to form a second imprint in the medium,the second imprint defining a further part of the working templatepattern, and to cause the working template to contact a secondimprintable medium on a device substrate to form an imprint in thesecond medium corresponding to the working template pattern.
 63. Theapparatus according to claim 62, further comprising an etching apparatusconfigured to etch areas of reduced thickness of the first and secondimprints to expose regions of the working template substrate.
 64. Theapparatus according to claim 63, wherein the etching apparatus isconfigured to etch areas of reduced thickness of the imprint in thesecond medium to expose regions of the device substrate.